Discharge lamp lighting device and illumination device

ABSTRACT

This invention provides a discharge lamp lighting device and illumination device which can be miniaturized with high power factor and also is inexpensive. In the discharge lamp lighting device, in response to the zero crossing detected signal of a commercial AC power source detected by a detecting section, a voltage boosting/dropping circuit boosts or drops the commercial AC power source full-wave rectified by a rectifying circuit so that the current flowing through the discharge lamp is larger in the vicinity of the phases of 90° and 270° of the commercial AC power source than in the vicinity of the phases of 0° and 180° thereof, and a polarity changing circuit changes the polarity of the boosted or dropped current to be supplied to the discharge lamp. An illumination device is provided with such a discharge lamp lighting device.

TECHNICAL FIELD

This invention relates to a discharge lamp lighting device with a powersource of an commercial AC and an illumination device equipped with thedischarge lamp lighting device, and more particularly to those capableof lighting the discharge lamp with high power factor.

BACKGROUND OF THE INVENTION

Referring to FIG. 9, an explanation will be given of a conventionaldischarge lamp device. FIG. 9 is a circuit diagram of a conventionaldischarge lamp device which is disclosed in e.g. JP-A-9-45490.

In FIG. 9, reference numeral 101 denotes a commercial power source; 102a rectifying circuit; 103 a voltage boosting inverter; 104 a voltagedropping inverter; 105 a square wave circuit; 106 a starting circuit;107 a discharge lamp; 108 a voltage-boosting inverter control circuit;109 a voltage-dropping inverter control circuit; 110 a square wavecontrol circuit; and 111 a control power source circuit.

Referring to the drawing, an explanation will be given of the operationof the conventional discharge lamp device. When electric power issupplied from a commercial A.C. power source 101, the control powersource circuit 111 creates control power which is fed to thevoltage-boosting inverter circuit 108, voltage dropping circuit 109 andsquare-wave control circuit 110. As a result, these circuits start tooperate.

First, the AC power from the commercial AC power source 101 is rectifiedby the rectifying circuit 102, and the rectified power is applied to thevoltage boosting inverter 103. The voltage-boosting inverter 103converts the applied DC voltage into a DC voltage of 400 V. Then, thevoltage boosting inverter control circuit 108 corrects wave distortionof an input current supplied to the voltage-boosting inverter 103 tocontrol the voltage-boosting inverter 103 so that the input power factoris approximately 100%.

Next, the voltage-dropping inverter 104 inverts the DC voltage suppliedfrom the voltage-boosting inverter 103 into a DC voltage correspondingto a load change in the discharge lamp 107. Then, thevoltage-dropping-inverter control circuit 109 controls the outputvoltage from the voltage dropping inverter 104 so that the currentflowing through the discharge lamp 107 is a prescribed current, e.g. aconstant current of 2 A.

The square wave circuit 105 converts the DC voltage applied from thevoltage dropping inverter 104 into an AC square wave. Then, the squarewave control circuit 110 controls the square wave circuit 105 so thatthe current flowing through the discharge lamp 107 is an AC square waveat a prescribed frequency of e.g. 100 Hz.

The starting circuit 106 generates a high voltage pulse by the AC squarewave from the square wave circuit 105 to start the lighting of thedischarge lamp 107.

The discharge lamp device which has a low power factor exerts anadverseeffect on a commercial AC power system facility so that the dischargelamp device with a high power factor has been demanded. In order to givethe high power factor to the device, as in the conventional dischargelamp device, using the voltage boosting inverter 103, the AC voltagemust be converted into a DC voltage.

However, where the discharge lamp device is equipped with thevoltage-boosting inverter 103, since the voltage-boosting inverter 103itself is bulky, heavy and expensive, the discharge lamp device alsobecomes bulky, heavy and expensive.

This invention has been accomplished in order to solve the problemdescribed above, and intends to provide a discharge lamp lighting deviceand illumination device which can be miniaturized with a high powerfactor and also is inexpensive.

DISCLOSURE OF THE INVENTION

The discharge lamp lighting device according to this invention ischaracterized by comprising:

a rectifying circuit for full-wave rectifying a commercial AC powersource;

a voltage boosting/dropping circuit for boosting or dropping a voltagefrom the rectifying circuit;

a control section for controlling the boosted/dropped voltage from thevoltage boosting/dropping circuit;

a polarity changing circuit for changing the polarity of the currentboosted or dropped by the voltage boosting/dropping circuit;

a discharge lamp through which the current from the polarity changingcircuit is passed; and

a detecting section for detecting the zero crossing of the commercial ACpower source, and in that

in response to a zero-crossing detected signal detected by the detectingsection, the control section controls the voltage boosting/droppingcircuit so that the current flowing through the discharge lamp is largerin the vicinity of the phases of 90° and 270° of the commercial AC powersource than in the vicinity of the phases of 0° and 180° thereof.

The discharge lamp lighting device according to this invention is alsocharacterized in that when the polarity of the current passed throughthe discharge lamp by the polarity changing circuit is changed at afrequency equal to or higher than that of the commercial AC powersource, it is changed at least in the vicinity of the phases of 0° and180° thereof.

The discharge lamp lighting device according to this invention is alsocharacterized in that when the polarity of the current passed throughthe discharge lamp by the polarity changing circuit is changed at afrequency equal to or higher than that of the commercial AC powersource, it is changed at least in the vicinity of the phases of 90° and270° thereof.

The discharge lamp lighting device according to this invention is alsocharacterized in that the detecting section has a function of detectingthe phase of the commercial AC power source, and the control sectioncontrols the voltage boosting/dropping circuit and the polarity changingcircuit changes the polarity of the flowing current so that the currentflowing through the discharge lamp is substantially in phase with thatof the commercial AC power source voltage and has a substantially sinewaveform.

The discharge lamp lighting device according to this invention is alsocharacterized in that the current flowing through the discharge lamp isconstant in the vicinity of the phases of 90° and 270°.

The discharge lamp lighting device according to this invention is alsocharacterized in that the current flowing through the discharge lamp isthe square of the sine wave in synchronism with the commercial AC powersource voltage.

The discharge lamp lighting device according to this invention is alsocharacterized by further comprising a voltage detecting section fordetecting the voltage across the discharge lamp, and in that in responseto the detected value from the voltage detecting section, the controlsection controls the voltage boosting/dropping circuit so that electricpower supplied to the discharge lamp is constant.

The illumination device according to this invention is characterized byhaving a discharge lamp lighting device defined in any one of thedischarge lamp lighting device described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an arrangement of a discharge lamplighting device according to the first and second embodiments of thisinvention;

FIG. 2 is a waveform chart showing the operation of the discharge lamplighting device according to the first embodiment of this invention;

FIG. 3 is a waveform chart showing the operation of the discharge lamplighting device according to the second embodiment of this invention;

FIG. 4 is a block diagram showing an arrangement of a discharge lamplighting device according to the third embodiment of this invention;

FIG. 5 is a block diagram showing an arrangement of a discharge lamplighting device according to the fourth embodiment of this invention;

FIG. 6 is a block diagram showing an arrangement of a discharge lamplighting device according to the fifth embodiment of this invention;

FIG. 7 is a waveform chart showing the operation of the discharge lamplighting device according to the sixth embodiment of this invention;

FIG. 8 is a waveform chart showing the operation of the discharge lamplighting device according to the seventh embodiment of this invention;and

FIG. 9 is a circuit diagram showing a conventional discharge lamplighting device.

BEST MODE OF CARRYING OUT THE INVENTION

Now referring to the drawings, an explanation will be given ofrespective embodiments of this invention.

FIRST EMBODIMENT

Now referring to FIGS. 1 and 2, an explanation will be given of adischarge lamp lighting device according to the first embodiment of thisinvention. FIG. 1 is a block diagram showing an arrangement of adischarge lamp lighting device according to the first embodiment of thisinvention, and FIG. 2 is a waveform chart showing the operation of thedischarge lamp lighting device according to the first embodiment of thisinvention.

In FIG. 1, reference numeral 1 denotes a commercial AC power source; 2 arectifying circuit of a diode bridge which serves to full-wave rectify acommercial AC voltage; and 3 a voltage boosting/dropping converter forboosting or dropping the full-wave rectified voltage. The voltageboosting/dropping converter 3 includes a switching element 3 a, atransformer 3 b, a diode 3 c and a capacitor 3 d.

Reference numeral 4 denotes a current detecting resistor for detecting acurrent flowing through a discharge lamp 6, and reference numeral 5denotes a polarity-changing circuit for changing the polarity of thecurrent flowing through a discharge lamp 6. The polarity-changingcircuit 5 includes a switching element 5 a, a switching element 5 b, aswitching element 5 c and a switching element 5 d. Reference numeral 6denotes a discharge lamp; 7 a starting pulse generating circuit forgenerating a high voltage pulse to start the discharge lamp; and 8 acontrol power source creating circuit for creating a control powersource.

Reference numeral 9 denotes a control circuit which includes a detectingunit 9 a for detecting a zero-crossing of a commercial AC, a controlunit 9 b for controlling the voltage boosting/dropping converter 3, acurrent detecting unit 9 c for detecting the current flowing through thedischarge lamp 6 based on the current detecting resistor 4, a startingpulse control unit 9 d for controlling the starting pulse generatingcircuit 7, a target current computing unit 9 e and a control unit 9 ffor controlling the polarity changing circuit 5.

In FIG. 2, (a) shows a current/voltage waveform of the commercial ACpower source 1; (b) shows an ON/OFF state of the switching element 5 aand a switching element 5 d of the polarity changing circuit 5; (c)shows an ON/OFF state of the switching element 5 b and a switchingelement 5 c of the polarity changing circuit 5; (d) shows a targetcurrent computed by the target current computing unit 9 e; and (e) showsa current flowing through the discharge lamp 6.

Now referring to the drawings, an explanation will be given of theoperation of the discharge lamp lighting device according to the firstembodiment of this invention.

When electric power is supplied from the commercial AC power source 1,the control power source creating circuit 8 creates the control powersource to be supplied to the control circuit 9. Then, the controlcircuit 9 starts to operate. In the control circuit 9, the startingpulse control unit 9d controls the starting pulse generating circuit 7,which in turn supplies a high voltage pulse to the discharge lamp 6.Then, the discharge lamp is lit.

When the discharge lamp is lit, a current starts to flow to the currentdetecting resistor 4. This current is detected by the current detectingunit 9 c. On the other hand, the target current computing unit 9 ecomputes the target current. The control unit 9 b compares the currentdetected by the current detecting unit 9 c and the target currentcomputed by the target current computing unit 9 e and controls thevoltage boosting/dropping converter 3 so that the detected current andthe target current become equal to each other, thereby making feedbackcontrol.

In the voltage boosting/dropping conveter 3, the switching element 3 arepeats ON/OFF at a high frequency of several tens of kHz. When theswitching element 3 a is “ON”, a current flows to the primary side ofthe transformer 3 b where energy is stored. On the other hand, when theswitching element 3 a is “OFF”, the stored energy is discharged to thesecondary side of the transformer 3 b as electric power. Since thedischarged electric power is at a high frequency of several tens kHz,the high frequency component is removed by the diode 3 c and thecapacitor 3 d, and the resultant power is supplied to the discharge lamp6.

Therefore, where the target current from the target current computingunit 9 e is smaller than the detected current from the current detectingunit 9 c, the control unit 9 b increases the time of “ON” of theswitching element 3 a thereby to increase the electric power to bedischarged to the secondary side, thereby increasing the current flowingthrough the discharge lamp 6. Where the detected current is larger thanthe target current, the control unit 9 b decreases the time of “ON” ofthe switching element 3 a to decrease the electric power to bedischarged to the secondary side, thereby decreasing the current flowingthrough the discharge lamp 6. These operations are performed at a highspeed so that the current flowing through the discharge lamp is equal tothe target current.

The control unit 9 f controls the polarity changing circuit 5 so that aset of the switching elements 5 a and 5 d and another set of theswitching elements 5 c and 5 b are alternately turned ON. Thus, the DCcurrent from the voltage boosting/dropping converter 3 is converted intoan AC current, which flows through the discharge lamp 6.

Then, the detecting unit 9 a produces a zero-crossing detected signalwhen the voltage in the commercial AC becomes zero volt in its periodicchange.

In response to the zero-crossing detected signal from the detecting unit9 a, the target current computing unit 9 e computes the target currenton the basis of the commercial AC voltage waveform as shown in FIG. 2(a)so that it is small in the vicinity of 0° and 180° and large in thevicinity of 90° and 270° as shown in FIG. 2(d).

In response to the zero-crossing detected signal from the detecting unit9 a, the control unit 9 f changes the set of the switching elements 5 aand 5 d between their “ON” and “OFF” as shown in FIG. 2(b) and changesthe switching elements 5 c and 5 b between their “ON” and “OFF” as shownin FIG. 2(c).

Thus, as shown in FIG. 2(e), the current flowing through the dischargelamp 6 becomes a sinusoidal wave current whose polarity is changed at 0°and 180° and synchronous with the commercial AC power source 1 shown inFIG. 2(a). The current flowing into the discharge lamp lighting devicefrom the commercial AC power source 1 is proportional to the currentflowing through the discharge lamp 6. Therefore, the input current forthe discharge lamp lighting device is also the sinusoidal wave currentsynchronous with the commercial AC power source 1, thereby increasingthe input power factor. Further, unneccessity of a power factorimproving circuit such as a voltage boosting inverter can provides acompact and inexpensive discharge lamp lighting device.

SECOND EMBODIMENT

Referring to FIGS. 1 and 3, an explanation will be given of thedischarge lamp lighting device according to the second embodiment ofthis invention. FIG. 1 is a block diagram showing an arrangement of adischarge lamp lighting device according to the second embodiment ofthis invention, which is the same as that of the first embodiment. FIG.3 is a waveform chart showing the operation of the discharge lamplighting device according to the second embodiment of this invention.

In FIG. 3, (a) shows a current/voltage waveform of the commercial ACpower source 1; (b) shows a light flux discharged from the dischargelamp 6 before improvement; (c) shows an ON/OFF state of the switchingelement 5 a and a switching element 5 d of the polarity changing circuit5; (d) shows an ON/OFF state of the switching element 5 b and aswitching element 5 c of the polarity changing circuit 5; (e) shows atarget current computed by the target current computing unit 9 e; (f)shows a current flowing through the discharge lamp 6; and (g) shows alight flux discharged from the discharge lamp 6 after improvement.

In the first embodiment, the polarity of the current which is to bepassed through the discharge lamp 6 is changed at 0° and 180° of thecommercial AC power source as shown in FIG. 2(e). In this case, the sizeof the light flux discharged from the discharge lamp 6 provides a leveldifference between the polarities as shown in FIG. 3(b). Such aphenomenon is attributable to the fact that there is a difference in thelight emission efficiency between the polarities even when the currentwith the same value between the positive and negative polarities ispassed through the discharge lamp. Connecting the peak of the lightfluxes in FIG. 3(b) gives a pulsating wave a shown by the line (i).Human's eyes are susceptible to such a pulsating wave at a low frequencyas flicker.

Therefore, in accordance with the second embodiment, the control unit 9f controls the polarity changing circuit 5 so that for the commercial ACvoltage waveform of FIG. 3(a), the ON/OFF states of a set of theswitching elements 5 a and 5 b and of another set of the switchingelements 5 b and 5 c are changed at 90° and 270° as shown in FIG. 3(c)and FIG. 3(d), respectively. Thus, the polarity of the target currentshown in FIG. 3(e) computed by the target current computing unit 9 e andproduced from the voltage boosting/dropping converter 3 is changed bythe polarity changing circuit 5 as shown in FIG. 3(f). Thus, the currentwhich is small in the vicinity of 0° and 180° and large in the vicinityof 90° and 270° flows through the discharge lamp 6.

As a result, the current flowing through the discharge lamp 6 issubstantially in phase with the commercial AC power source voltage andits absolute value is controlled by the sinusoidal wave current. Thus,the size of the light flux discharged from the discharged lamp 6 is suchas shown in FIG. 3(g) and provides a uniform peak value. The human'seyes are difficult to susceptible to such a light flux as flicker ascompared with the first embodiment.

THIRD EMBODIMENT

Referring to FIG. 4, an explanation will be given of the discharge lamplighting device according to the third embodiment of this invention.FIG. 4 is a block diagram showing an arrangement of a discharge lamplighting device according to the third embodiment of this invention.

In FIG. 4, the current detecting resistor 4 is located between therectifying circuit 2 and the voltage boosting/dropping converter 3. Theremaining structure is the same as that of the discharge lamp lightingdevice according to the first embodiment or the second embodiment.

Referring to the drawings, an explanation will be given of the operationof the discharge lamp lighting device according to the third embodimentof this invention. The operation of the other arrangement than thecurrent detecting resistor 4 is the same as that in the discharge lamplighting device according to the first embodiment or second embodiment.

As regards the operation of the current detecting resistor 4, theresistor 4 was used to detect the discharge lamp current in thedischarge lamp lighting device according to the first embodiment or thesecond embodiment. On the other hand, in the third embodiment, theresistor 4 is used to detect the input current to the discharge lamplighting device. The target current is computed so that the detectedinput current is small in the vicinity of 0° and 180°, and large in thevicinity of 90° and 270°. The control unit 9 b controls the voltageboosting/dropping converter 3 so that the target current is equal to thedetected current from the current detecting unit 9 c, thereby makingfeedback control.

As a result, the input current for the discharge lamp lighting device isalso the sinusoidal wave current synchronous with the commercial ACpower source 1, thereby increasing the input power factor. Further,unneccessity of a power factor improving circuit such as a voltageboosting inverter can provides a compact and inexpensive discharge lamplighting device.

FOURTH EMBODIMENT

Referring to FIG. 5, an explanation will be given of the discharge lamplighting device according to the fourth embodiment of this invention.FIG. 5 is a block diagram showing an arrangement of a discharge lamplighting device according to the fourth embodiment of this invention.

In FIG. 5, reference numeral 9 g denotes a discharge lamp voltagedetecting unit provided in the control circuit 9. The remainingstructure is the same as that of the discharge lamp lighting deviceaccording to the first embodiment or the second embodiment.

Referring to FIG. 5, an explanation will be given of the operation ofthe discharge lamp lighting device according to the fourth embodiment ofthis invention. The operation of the other arrangement than thedischarge lamp voltage detecting unit 9 g is the same as that in thedischarge lamp lighting device according to the first embodiment orsecond embodiment.

As regards the operation of the control circuit 9, in response to thevoltage information of the discharge lamp 6 supplied from the dischargelamp voltage detecting unit 9 g, when the voltage of the discharge lamp6 is high, the target current computing unit 9 e decreases the amplitudeof the target current, for example, when the discharge lamp voltage is100 V, the amplitude of the target current is reduced to 1.5 A. When thevoltage of the discharge lamp 6 is low, the amplitude of the targetcurrent is increased, for example, when the discharge lamp voltage is 75V, the amplitude of the target current is increased to 2.0 A. Thecontrol unit 9 b controls the voltage boosting/dropping converter 3 sothat the target current is equal to the detected current from thecurrent detecting unit 9 c, thereby making feedback control.

As a result, the power supplied to the discharge lamp remains constantregardless with a difference in the discharge lamp voltage due to thesecular change of the discharge lamp and difference in bodies, and hencethe discharge lamp provide constant brightness.

FIFTH EMBODIMENT

Now referring to FIG. 6, an explanation will be given of a dischargelamp lighting device according to the fifth embodiment of thisinvention. FIG. 6 is a block diagram showing an arrangement of adischarge lamp lighting device according to the fifth embodiment of thisinvention.

In FIG. 6, reference numeral 1 denotes a commercial AC power source; 2 arectifying circuit of a diode bridge which serves to full-wave rectify acommercial AC voltage; and 3 a voltage boosting/dropping converter forboosting or dropping the full-wave rectified voltage. The voltageboosting/dropping converter 3 includes a switching element 3 a, atransformer 3 b, a diode 3 c, a diode 3 f, a capacitor 3 d and acapacitor 3 e.

Reference numeral 4 denotes a current detecting resistor for detecting acurrent flowing through a discharge lamp 6, and reference numeral 5denotes a polarity-changing circuit for changing the polarity of thecurrent flowing through a discharge lamp 6. The polarity-changingcircuit 5 includes a switching element 5 a and a switching element 5 b.Reference numeral 6 denotes a discharge lamp; 7 a starting pulsegenerating circuit for generating a high voltage pulse to start thedischarge lamp 6; and 8 a control power source creating circuit forcreating a control power source.

Reference numeral 9 denotes a control circuit which includes a detectingunit 9 a for detecting a zero-crossing of a commercial AC, a controlunit 9 b for controlling the voltage boosting/dropping converter 3, acurrent detecting unit 9 c for detecting the current flowing through thedischarge lamp 6 based on the current detecting resistor 4, a startingpulse control unit 9 d for controlling the starting pulse generatingcircuit 7, a target current computing unit 9 e and a control unit 9 ffor controlling the polarity changing circuit 5.

Referring to the drawings, an explanation will be given of the operationof the discharge lamp lighting device according to the fifth embodimentof this invention.

First, when electric power is supplied from the commercial AC powersource 1, the control power source creating circuit 8 creates thecontrol power source to be supplied to the control circuit 9. Then, thecontrol circuit 9 starts to operate. In the control circuit 9, thestarting pulse control unit 9 d controls the starting pulse generatingcircuit 7, which in turn applies a high voltage pulse to the dischargelamp 6. Then, the discharge lamp 6 is lit.

When the discharge lamp 6 is lit, a current starts to flow through thecurrent detecting resistor 4. This current is detected by the currentdetecting unit 9 c. On the other hand, the target current computing unit9 e computes the target current. The control unit 9 b compares thecurrent detected by the current detecting unit 9 c and the targetcurrent computed by the target current computing unit 9 e and controlsthe voltage boosting/dropping converter 3 so that the detected currentand the target current become equal to each other, thereby makingfeedback control.

In the voltage boosting/dropping converter 3, the switching element 3 arepeats ON/OFF at a high frequency of several tens of kHz. When theswitching element 3 a is “ON”, a current flows to the primary side ofthe transformer 3 b where energy is stored. On the other hand, when theswitching element 3 a is “OFF”, the stored energy is discharged to thesecondary side of the transformer 3 b as electric power.

In this case, if the high frequency component of the switching element 5a of the polarity changing circuit 5 is “ON”, the discharged electricpower at a high frequency of several tens kHz is removed by the diode 3c, and the capacitor 3 d and the current flows in a direction of arrow(a) in FIG. 6. On the other hand, if the switching element 5 b of thepolarity changing circuit 5 is “ON”, the high frequency component of thedischarged electric power at a high frequency of several tens kHz isremoved by the diode 3 f and the capacitor 3 e, and the current flows ina direction of arrow (b) in FIG. 6.

Thus, where the target current from the target current computing unit 9e is smaller than the detected current from the current detecting unit 9c, the control unit 9 b increases the time of “ON” of the switchingelement 3 a thereby to increase the electric power to be discharged tothe secondary side, thereby increasing the current flowing through thedischarge lamp 6. Where the detected current is larger than the targetcurrent, the control unit 9 b decreases the time of “ON” of theswitching element 3 a to decrease the electric power to be discharged tothe secondary side, thereby decreasing the current flowing through thedischarge lamp 6. These operations are performed at a high speed so thatthe current flowing through the discharge lamp is equal to the targetcurrent.

The control unit 9 f controls the polarity changing circuit 5 so thatthe switching elements 5 a and 5 b are alternately turned ON. Thus, anAC current flows through the discharge lamp 6. The detecting unit 9 adetects zero-crossings and the period between the zero-crossings of thecommercial AC power source 1. In response to the zero-crossing detectedsignal produced from the detecting unit 9 a, the target currentcomputing unit 9 e computes the target current on the basis of thecommercial AC voltage waveform as shown in FIG. 2(a) so that it is smallin the vicinity of 0° and 180° and large in the vicinity of 90° and 270°as shown in FIG. 2(d).

In response to the zero-crossing detected signal from the detecting unit9 a, as in the first embodiment, the control unit 9 f changes theswitching element between the switching elements 5 a and 5 b at 0° and180° of the commercial AC power source so that the current flowingthrough the discharge lamp 6 is inverted at 0° and 180°.

Thus, the current flowing through the discharge lamp 6 becomes asinusoidal wave current which is synchronous with the commercial ACpower source 1. In addition, the current flowing into the discharge lamplighting device from the commercial AC power source 1 is proportional tothe current flowing through the discharge lamp 6. Therefore, the inputcurrent for the discharge lamp lighting device is also the sinusoidalwave current synchronous with the commercial AC power source 1, therebyincreasing the input power factor. Further, unneccessity of a powerfactor improving circuit such as a voltage boosting inverter canprovides a compact and inexpensive discharge lamp lighting device.

Otherwise, in response to the zero crossing detected signal, as in thesecond embodiment, the control unit 9 f changes the switching elementbetween the switching elements 5 a and 5 b at 90° and 270° of thecommercial AC power source power source so that the current flowingthrough the discharge lamp 6 is inverted at 90° and 270°.

Thus, the size of the light flux discharged from the discharged lamp 6provides a uniform peak value. The human's eyes are difficult tosusceptible to such a light flux as flicker.

EMBODIMENT 6

Referring to FIG. 7, an explanation will be given of the discharge lamplighting device according to the sixth embodiment of this invention.FIG. 7 is a waveform chart showing the operation of the discharge lamplighting device according to the sixth embodiment of this invention.

In FIG. 7, (a) shows a current/voltage of the commercial AC voltage ofthe commercial AC power source 1; (b) shows a target current computed bythe target current computing unit 9 e according to the first to fifthembodiments; and (c) shows the target current computed by the targetcomputing unit 9 e according to this embodiment, which is flat in thevicinity of 90° and 270°.

In this embodiment, the other operation than that as illustrated in FIG.7(c) is the same as that in the first to fifth embodiments.

In this embodiment, the target current computing unit 9 e computes thetarget current shown in FIG. 7(c). The control unit 9 b compares thecurrent detected by the current detecting unit 9 c and the targetcurrent computed by the target current computing unit 9 e and controlsthe voltage boosting/dropping converter 3 so that the detected currentand the target current become equal to each other, thereby makingfeedback control.

Thus, the peak the light flux becomes flat like the current waveform sothat the human's eyes are further difficult to susceptible to such alight flux as flicker.

SEVENTH EMBODIMENT

Referring to FIG. 8, an explanation will be given of the discharge lamplighting device according to the seventh embodiment of this invention.FIG. 8 is a waveform chart showing the operation of the discharge lamplighting device according to the sixth embodiment of this invention.

In FIG. 8, (a) shows a discharge lamp current waveform; and (b) shows adischarge lamp voltage waveform. In this embodiment, the other operationthan that illustrated in FIG. 8 is the same as that in the first tosixth embodiments.

As apparent from FIG. 8, the discharge lamp voltage provides jumps dueto a reignition voltage at the points where the discharge lamp currentis small. In the other region, the discharge lamp voltage exhibits aconstant voltage characteristic.

Assuming that the discharge lamp voltage is a prescribed constantvoltage A and the commercial AC voltage is represented by V·sin θ, inorder that the current flowing from the commercial AC power source intothe discharge lamp lighting device has a waveform of I·sin θ which issynchronous with the commercial AC power source voltage, it is desirablethat the discharge lamp current may have a waveform of square of sin θon the basis of an equation of V·sin θ×I·sin θ=A×discharge lamp current.In this case, the input current provides a waveform of sin θ synchronouswith the commercial AC power source voltage so that it provides leastdistortion of the input current and improves the power factor.

The target current computing unit 9 e computes the target current of thesquare of sin θ. The control unit 9 b compares the current detected bythe current detecting unit 9 c and the target current computed by thetarget current computing unit 9 e and controls the voltageboosting/dropping converter 3 so that the detected current and thetarget current become equal to each other, thereby making feedbackcontrol.

The first to seventh embodiments have been explained in connection withthe discharge lamp lighting device. However, where these discharge lamplighting device is attached to an illumination device, the illuminationdevice which gives less flicker, is inexpensive and compact can beprovided.

Industrial Applicability

As described above, the discharge lamp lighting device according to thisinvention is characterized by comprising:

a rectifying circuit for full-wave rectifying a commercial AC powersource;

a voltage boosting/dropping circuit for boosting or dropping a voltagefrom the rectifying circuit;

a control section for controlling the boosted/dropped voltage from thevoltage boosting/dropping circuit;

a polarity changing circuit for changing the polarity of the currentboosted or dropped by the voltage boosting/dropping circuit;

a discharge lamp through which the current from the polarity changingcircuit is passed; and

a detecting section for detecting the zero crossing of the commercial ACpower source, and in that

in response to the zero-crossing detected signal detected by thedetecting section, the control section controls the voltageboosting/dropping circuit so that the current flowing through thedischarge lamp is larger in the vicinity of the phases of 90° and 270°of the commercial AC power source than in the vicinity of the phases 0°and 180° thereof. In such a configuration, the input current for thedischarge lamp lighting device is synchronous with the commercial ACvoltage, thereby increasing the input power factor. Therefore, withoutusing a power factor improving circuit such as a voltage boostinginverter, the discharge lamp lighting device can have an increased inputpower factor and can be made compact and inexpensive.

As described above, the discharge lamp lighting device according to thisinvention is also characterized in that when the polarity of the currentpassed through the discharge lamp by the polarity changing circuit ischanged at a frequency equal to or higher than that of the commercial ACpower source, it is changed at least in the vicinity of the phases of 0°and 180° thereof. In this configuration, since the current flowingthrough the discharge lamp when the polarity is changed is approximatelyzero, there is no loss of changing the polarity so that noise occurrenceis also suppressed, thereby realizing the high efficiency of thelighting device.

Further, as described above, the discharge lamp lighting deviceaccording to this invention is also characterized in that when thepolarity of the current passed through the discharge lamp by thepolarity changing circuit is changed at a frequency equal to or higherthan that of the commercial AC power source, it is changed at least inthe vicinity of the phases of 90° and 270° thereof. In thisconfiguration, a difference in the peaks of the fluxes which isattributable to the light emitting efficiency of the discharge lampaccording to the polarity is removed, thereby reducing flicker.

The discharge lamp lighting device according to this invention is alsocharacterized in that the detecting section has a function of detectingthe phase of the commercial AC power source, and the control sectioncontrols the voltage boosting/dropping circuit and the polarity changingcircuit changes the polarity of the flowing current so that the currentflowing through the discharge lamp is substantially in phase with thatof the commercial AC power source voltage and has a substantially sinewaveform. In this configuration, the current flowing from the commercialAC power source into the discharge lamp lighting device has also sinewaveform, thereby reducing the distortion thereof.

As described above, the discharge lamp lighting device according to thisinvention is also characterized in that the current flowing through thedischarge lamp is constant in the vicinity of the phases of 90° and270°. Therefore, the peak of the light flux becomes flat in an increasedregion, thereby reducing flicker.

As described above, the discharge lamp lighting device according to thisinvention is also characterized in that the current flowing through thedischarge lamp is the square of the sine wave in synchronism with thecommercial AC power source voltage. Therefore, the input current has asine waveform in synchronism with the commercial AC power source voltageso that it provides least distortion and improves the power factor.

As described above, the discharge lamp lighting device according to thisinvention is also characterized by further comprising a voltagedetecting section for detecting the voltage across the discharge lamp,and in that in response to the detected value of the voltage detectedsection, the control section controls the voltage boosting/droppingcircuit so that electric power supplied to the discharge lamp isconstant. In this configuration, the power supplied to the dischargelamp remains constant regardless with a difference in the discharge lampvoltage due to the secular change of the discharge lamp and differencein bodies, and hence the discharge lamp provides constant brightness.

As described above, the illumination device is characterized by having adischarge lamp lighting device defined in any one of the discharge lamplighting device described above. Therefore, the illumination devicewhich gives less flicker, is inexpensive and compact can be provided.

What is claimed is:
 1. A discharge lamp lighting device comprising: arectifying circuit for full-wave rectifying a commercial AC powersource; a voltage boosting/dropping circuit for boosting or dropping avoltage from the rectifying circuit; a control section for controllingthe boosted/dropped voltage from the voltage boosting/dropping circuit;a polarity changing circuit for changing polarity of a current boostedor dropped by the voltage boosting/dropping circuit; a discharge lampthrough which the current from the polarity changing circuit is passed;and a detecting section for detecting a zero crossing of the commercialAC power source, wherein in response to the zero-crossing detectedsignal detected by the detecting section, the control section controlsthe voltage boosting/dropping circuit so that the current flowingthrough the discharge lamp is larger in the vicinity of the phases of90° and 270° of the commercial AC power source than in the vicinity ofthe phases of 0° and 180° thereof.
 2. The discharge lamp lighting deviceaccording to claim 1, further comprising a voltage detecting section fordetecting the voltage across the discharge lamp, wherein in response tothe detected value from the voltage detected section, the controlsection controls the voltage boosting/dropping circuit so that electricpower supplied to the discharge lamp is constant.
 3. An illuminationdevice having a discharge lamp lighting device defined in claim
 1. 4.The discharge lamp lighting device according to claim 1, wherein whenthe polarity of the current passed through the discharge lamp by thepolarity changing circuit is changed at a frequency equal to or higherthan that of the commercial AC power source, it is changed at least inthe vicinity of the phases of 0° and 180° thereof.
 5. The discharge lamplighting device according to claim 4, wherein the detecting section hasa function of detecting the phase of the commercial AC power source, andthe control section controls the voltage boosting/dropping circuit andthe polarity changing circuit changes the polarity of the flowingcurrent so that the current flowing through the discharge lamp issubstantially in phase with that of the commercial AC power sourcevoltage and has a substantially sine waveform.
 6. The discharge lamplighting device according to claim 4, further comprising a voltagedetecting section for detecting the voltage across the discharge lamp,wherein in response to the detected value from the voltage detectedsection, the control section controls the voltage boosting/droppingcircuit so that electric power supplied to the discharge lamp isconstant.
 7. An illumination device having a discharge lamp lightingdevice defined in claim
 4. 8. The discharge lamp lighting deviceaccording to claim 1, wherein when the polarity of the current passedthrough the discharge lamp by the polarity changing circuit is changedat a frequency equal to or higher than that of the commercial AC powersource, it is changed at least in the vicinity of the phases of 90° and270° thereof.
 9. The discharge lamp lighting device according to claim8, wherein the detecting section has a function of detecting the phaseof the commercial AC power source, and the control section controls thevoltage boosting/dropping circuit and the polarity changing circuitchanges the polarity of the flowing current so that the current flowingthrough the discharge lamp is substantially in phase with that of thecommercial AC power source voltage and has a substantially sinewaveform.
 10. The discharge lamp lighting device according to claim 8,further comprising a voltage detecting section for detecting the voltageacross the discharge lamp, wherein in response to the detected valuefrom the voltage detected section, the control section controls thevoltage boosting/dropping circuit so that electric power supplied to thedischarge lamp is constant.
 11. An illumination device having adischarge lamp lighting device defined in claim
 8. 12. The dischargelamp lighting device according to claim 1, wherein the detecting sectionhas a function of detecting the phase of the commercial AC power source,and the control section controls the voltage boosting/dropping circuitand the polarity changing circuit changes the polarity of the flowingcurrent so that the current flowing through the discharge lamp issubstantially in phase with that of the commercial AC power sourcevoltage and has a substantially sine waveform.
 13. The discharge lamplighting device according to claim 12, further comprising a voltagedetecting section for detecting the voltage across the discharge lamp,wherein in response to the detected value from the voltage detectedsection, the control section controls the voltage boosting/droppingcircuit so that electric power supplied to the discharge lamp isconstant.
 14. An illumination device having a discharge lamp lightingdevice defined in claim
 12. 15. The discharge lamp lighting deviceaccording to claim 12, wherein the current flowing through the dischargelamp is constant in the vicinity of the phases of 90° and 270°.
 16. Thedischarge lamp lighting device according to claim 15, further comprisinga voltage detecting section for detecting the voltage across thedischarge lamp, wherein in response to the detected value from thevoltage detected section, the control section controls the voltageboosting/dropping circuit so that electric power supplied to thedischarge lamp is constant.
 17. An illumination device having adischarge lamp lighting device defined in claim
 15. 18. The dischargelamp lighting device according to claim 12, wherein the current flowingthrough the discharge lamp is the square of the sine wave in synchronismwith the commercial AC power source voltage.
 19. The discharge lamplighting device according to claim 18, further comprising a voltagedetecting section for detecting the voltage across the discharge lamp,wherein in response to the detected value from the voltage detectedsection, the control section controls the voltage boosting/droppingcircuit so that electric power supplied to the discharge lamp isconstant.
 20. An illumination device having a discharge lamp lightingdevice defined in claim 18.